1. Field of the Invention
The present invention relates to skimmer mechanisms installed in clarifier tanks to remove scum and debris floating on top of the water in the tank. More specifically, this invention relates to skimmer mechanisms configured for use in rectangular basins or clarifier tanks having chain and flight mechanisms.
2. State of the Art
Clarifier tanks are used in waste water systems and other effluent systems for processing effluent to remove solids and particulate matter from the fluid. Fluid entering into the tank is treated to facilitate aggregation and precipitation of particulate matter which sinks to the bottom of the tank. Floatable matter rises to the top of the water and must be skimmed off or otherwise removed. It is vital to remove the scum or floating debris from the water to reduce or prevent unpleasant odors. Clarification systems may include as basic features a tank for receiving the effluent, a skimmer mechanism on the bottom of the tank to sweep scum off the tank bottom, a skimmer arm on the top of the water to skim floating debris therefrom and outlet means for removing clarified water from the tank.
Round clarifier tanks typically employ skimmer arms which are rotatably secured to a center pier or pipe, which are positioned at the water level in the tank and which sweep out a radius about the tank. The skimmer arms generally include an arm and a blade or planar flap extending down from the arm. As the skimmer arm sweeps the radius of the tank, the blade or flap skims along the surface of the water and moves floating debris along in the sweep. The collected floating debris is directed toward a scum trough positioned on or near the outer wall of the tank. The scum entering the trough is carried away from the tank through associated pipe systems.
In rectangular tanks, two means for removing scum and floatables from the water surface are typically used. The most commonly used means is a trough or pipe which is positioned to extend from wall to wall across the short width of the tank. The trough has an open top (or the pipe may have a slotted opening) which is positioned at or near the water level. Scum or debris floating on the water's surface moves with the motion of the water and eventually drifts toward the trough or pipe (when tilted) and spills into its open top. The collected scum is removed from the trough by outlet pipe means connected to the trough and directed externally to the tank.
The other common means of removing scum and floating debris in rectangular tanks includes a chain and flight mechanism mounted to the inner surface of the two long walls of the tank. That is, sprocket wheels are generally secured to the inside surface of the long walls at the four comers of each wall. A chain is wound about the four sprocket wheels on each wall. A flight is interconnected between the two aligned chains and spans the width of the tank. The chains are positioned in the tank so that the flight interconnected between them is positioned during its rotation at about the level of water in the tank. The flight comprises an upper portion which extends away from the chain and may also include a skimmer blade projecting downwardly from the upper portion.
The chains are caused to rotate simultaneously in a single direction. The flight moves with the chains and when at the top of the tank, sweeps along the water surface in the tank gathering scum and floating debris as it moves. A trough positioned across the width of the tank, between the two longitudinal walls, is positioned to receive the debris moved along by the flight. As the chains continue to rotate, the flight moves into the water until the flight rounds the nearest sprocket wheel in the bottom of the tank. The flight then moves along the bottom of the tank and may act to skim sunken scum along the tank bottom toward a scum trough located in the bottom of the tank. The flight continues to move from the bottom of the tank to the top of the tank as the chains rotate about the sprocket wheels.
Chain and flight mechanisms used in rectangular clarifier tanks may include more than one flight and may be caused to rotate slower or faster to increase or decrease the removal of scum, or to produce a drier or wetter scum, as desired.
The chain and flight mechanisms presently used in rectangular clarifier tanks are problematic in that they tend to become overloaded with scum as they move along the water surface, resulting in the scum sinking into the water under its own weight. Scum which sinks back into the water degrades the clarity of the effluent and results in an increase in undesirable odors emanating from the tank. The flight members are also not positioned to optimally catch all of the floating debris and may become useless if the water level in the tank drops. Chain and flight mechanisms also require human intervention to assure proper increase or decrease in rotation of the chain mechanism.
Therefore, it would be an improvement in the art to provide a chain and flight mechanism having a skimmer means which is capable of collecting sizable amounts of scum or floating debris without losing the debris from under the skimmer. It would be a further improvement in the art to provide a skimming mechanism which is adaptable to small fluctuating water levels within the tank.